This disclosure relates to generating control signals for memory devices.
A conventional memory device, such as a flash memory, can comprise a series of bit lines arranged in columns. Each bit line, in turn, is connected to a series of memory strings, and each memory string includes several memory locations, e.g., M1 . . . Mq, that correspond to bit locations. Each memory string has one end coupled to a corresponding bit line by a bit line selector, and another end coupled to a ground selector. Typically the bit lines selector and the ground selector comprise transistors.
The columnar architecture of the bit lines and memory strings results in numerous parallel memory locations. Each memory location has in input terminal, e.g., a gate, and the memory locations are grouped in a row-like fashion by connecting the respective gates of each group of memory locations to a corresponding word line.
To program a selected memory location in the memory device, a memory string that includes the selected memory location is selected by coupling the memory string to a reference voltage, e.g., a ground voltage applied to the bit line, and the input to the memory location is coupled to a program voltage applied to the word line for a period of time sufficient to program the selected memory location. Another voltage of a lesser magnitude, e.g., a pass voltage, is applied to the word lines of memory locations in the memory string that are not to be programmed. Because the memory locations are grouped by rows defined by the word line, however, memory locations in parallel memory strings will also receive the program voltage and pass voltage. To prevent programming in the parallel strings, the corresponding bit line selectors and ground selectors are kept off. The resulting high impedance of the bit line selectors and the ground selectors allows the unselected memory strings to float in response to the capacitive coupling of the world line voltages. This technique, known as “channel boosting,” prevents the memory locations in the unselected string from being programmed.
To ensure channel boosting, the bit line selectors corresponding to boosted channels must be kept off. The gate voltages of the bit line selectors, however, may be affected by the capacitive coupling with the word lines. Such coupling can cause the bit line selectors that are supposed to be in an off state to become conductive, resulting in a leakage current that discharges the boosted channel. Should the boosted channel discharge sufficiently, one or more corresponding memory locations may be inadvertently programmed, resulting in data corruption.